Grounding 2 separate services at same building - objectionable current question 250.6

[VladChiefns830]

Hello,
I have an engineer giving me grief, so I decided to redraw the design and ask the people here. I'm using 2017 NEC.
Picture a large building with 2 services at opposite ends of the building. I do realize that the services are not grouped at the same location, but there will be permanent placards per 230.2(E).
See picture.
Would we all agree that the services are connected to a COMMON GROUNDING ELECTRODE and that the services clearly meet NEC 250.58? I think most everyone here would agree...
??

 

[VladChiefns830]

So now for the question --
In order to make things "real safe" my designer added an extra "bonding jumper" BETWEEN Service 1 and Service 2.
He states that someone told him that all the electrical services on the building "need to be bonded together." My immediate reaction was that this conductor will contain a fair amount of neutral current, and I would consider it "objectionable" current per 250.6, at a minimum.
I could list other reasons why I would not do what is being shown in the picture below.
But I want to get input from others. Please see below:

 

[che12345]

Dear Mr.VladChiefns830
You had taken care of NEC 230.2.(e) also NEC 50.58 that cover the issue.
After going through dwg1 and dwg2, I wish to point out the following for your consideration:
1. In 1st dwg , the key item is the " common concreate-enclosed electrode" coloured green presumably NOT [visible for inspection]. In case there is a breakage due to whatever reason, that will end up to (grounding) [at two different points}, which is NOT allowed.
2. In 2nd dwg , the key item is the "extra bonding jumper" coloured red, presumably visible for inspection throughout the entire length. It ensures single point grounding.
3. I am not sure whether any part of NEC 250-xx stresses that the (common grounding conductor) [shall be visible for inspection through its entire length]?
Che Kuan Yau (Singapore)

 

[VladChiefns830]

Here are my responses for your consideration:
1. And how would a concrete-encased electrode "break?" I've never heard of one "breaking," ever. It's a concrete footing with steel bars, tied throughout. See 250.52.
2. "It ensures single-point grounding." We are talking about two (2) entirely separate services, with two (2) entirely separate service laterals.
3. "Visible for inspection during the entire length," wasn't part of the question.
But thanks for responding anyway.

 

[che12345]

Dear Mr. VladChiefns830 (Specifier/Regulator)(OP)15 Jun 22 12:19
"...Here are my responses for your consideration:
1. And how would a concrete-encased electrode "break?" I've never heard of one "breaking," ever. It's a concrete footing with steel bars, tied throughout. See 250.52.
2. "It ensures single-point grounding." We are talking about two (2) entirely separate services, with two (2) entirely separate service laterals.
3. "Visible for inspection during the entire length," wasn't part of the question...".
My personal opinion for your consideration:
1. Per NEC 250.52 Made and other electrodes.....one or more of the electrodes (b) through (d) shall be used....... Per 250.50 ..... the grounding electrode conductor shall be unspliced or by means of irreversible compression-type....or exothermic welding process...
Agreed that steel bar does NOT "break" physically , but they usually are NO making "good electrical contacts" i.e. = "break" electrically . Therefore, are NOT in compliance with 250.50.
2. With two separate services with two (2) entirely separate service laterals but to a single building needs additional attention.
3. It is very important to be visible including able to perform contact resistance test on joints throughout its entire length; even though wasn't part of the question , nor mentioned in NEC 250-xx.
Che Kuan Yau (Singapore)

 

[VladChiefns830]

1. Good point. But for the purposes of this discussion, assume that the grounding electrode conductor (GEC) is not spliced. It is a wire, which is connected to steel in the footing with the correct clamp, and inspected prior to the pour. That is what I have for this particular installation.
2. You say, "need attention." Can you elaborate?
3. It can be argued that the extra wire is not a GEC, therefore it doesn't need to be irreversible compression-type....or exothermic welding process... Let's assume for this discussion that the "extra bonding conductor" is visible and irreversible.

 

[che12345]

Dear Mr. VladChiefns830 (Specifier/Regulator)(OP)16 Jun 22 14:47
" 1. .... for the purposes of this discussion, assume that the grounding electrode conductor (GEC) is not spliced. It is a wire, which is connected to steel in the footing with the correct clamp, and inspected prior to the pour....
2. You say, "need attention." Can you elaborate?
3. It can be argued that the extra wire is not a GEC, therefore it doesn't need to be irreversible compression-type....or exothermic welding process... Let's assume for this discussion that the "extra bonding conductor" is visible and irreversible... ".
I am trying to understand NEC, as it is not the practice in my location.
1. " the grounding electrode conductor (GEC) is not spliced. It is a wire, which is connected to steel in the footing with the correct clamp, and inspected prior to the pour..." do not fulfill NEC 250-62 (c). Corrosion at clamping and breakage of conductor can happen. Visible inspection is not possible after pour.
2. See NEC 250-24 (3) Dual fed services....
The two separate feeds with their respective/separate protection/isolation means at the incoming, but (from the same one source) may be with different potentials. The 3ph1+N1 shall Not be connected with 3ph2+N2. However, the ground1 and ground2 shall be grounded at one point.
3. No. It is NOT an " extra extra wire is not a GEC..." All grounding conductors are GEC; not an extra to be taken lightly/superfluous.
Che Kuan Yau (Singapore)

 

[bacon4life]

I am picturing a large warehouse near me where the second service was added when the warehouse size was extended by 50%. Due to phased construction, I doubt there is a continuous metal path made up of structural metal and/or rebar between the two service locations. Even for a newly constructed warehouse, relying on dozens of structural joints and/or rebar spices to make an electrical connection between services 1000 ft apart seems rather dubious.

For services at the opposite ends of the building, how much current do expect to flow?

 

[VladChiefns830]

che,
It is not a dual fed service. It is not double-ended. I'm not being critical, but you don't seem to understand the configuration. In addition, you would be incorrect in that "All grounding conductors are grounding electrode conductors," if that is what you are stating.
But thanks for your participation and willingness to understand the NEC.

bacon,
No, that's not it. It is a brand new structure. It was all built at the same time. The services are connected to a COMMON GROUNDING ELECTRODE, which is the UFER (concrete-encased electrode). Code is satisfied at that point. Nobody is relying on "dozens of structural joints and/or rebar spices to make an electrical connection between services 1000 ft apart."

That extra wire isn't necessary and is in fact a code violation. It's remarkable that nobody has picked up on it.

 

[jghrist]

With or without the extra bonding wire, some neutral current can flow through the neutral of the opposite service back to the transformer. This is not desirable and may cause some electromagnetic interference. I don't think that the current would cause problems with GFCI breakers or receptacles as long as both neutral-ground bonds are at the service equipment.

Similarly, a ground fault would result in some fault current returning through the opposite service neutral, but should not cause misoperation of GFCI devices on the load side of the neutral-ground bonding jumpers.

The addition of an extra bonding jumper will increase flow of current through the opposite service neutral. I don't know if it is an NEC violation, and it could be required if there are other grounding electrodes connected to the UFER ground. See

https://www.ecmweb.com/national-ele...grounding-requirements-for-multiple-services.

"If separate services, feeders, or branch circuits supply a building, the same grounding electrode must be used [250.58]. Two or more grounding electrodes that are bonded together will be considered as a single grounding electrode system in this sense."

 

[VladChiefns830]

jghrist,

Today must be my lucky day, because I agree with what you say. There will be some neutral current on the grounding electrode system (this cannot always be avoided). But why make it worse? My point was - not to make it worse by installing that extra conductor between the services. I'm making them remove the extra bonding jumper per 250.6(1), (2), (3), etc. [2017 NEC]

 

[wayne440]

Claiming no expertise, if there is significant current on the "extra bonding jumper", I would not have a great deal of confidence in the efficiency of UFER ground connections.
Seems to me that the question might be better directed to the AHJ's electrical inspector- he/she will be the one who decides if the jumper is or is not required/desired/permitted.

 

[stevenal]

I don't see a second grounding electrode at either service. Does the ufer satisfy the 25 ohm requirement?

 

[bacon4life]

I think we just have different understandings about whether or not the entire building foundation is a single ufer ground. Although I do not have a specific citation that defines the maximum size of a ufer ground, I think it is reasonable to question whether a large warehouse foundation a single ufer ground. Even a new warehouse may have expansion joints between sections of the floor that would block electrical conductivity. considered a single ufer ground.

 

[jghrist]

If the foundation cannot be considered a single electrode, then Rule 250.58 would require the two electrodes to be bonded together to be considered a single electrode. Both services are required to be bonded to a single electrode. An external buried perimeter wire could be installed and bonded to each service ground to provide a single grounding electrode.

 

[VladChiefns830]

It's a CEE, one, common grounding electrode.

(3) Concrete-Encased Electrode. A concrete-encased electrode
shall consist of at least 6.0 m (20 ft) of either (1) or (2):
(1) One or more bare or zinc galvanized or other electrically
conductive coated steel reinforcing bars or rods of not
less than 13 mm (1∕2 in.) in diameter, installed in one
continuous 6.0 m (20 ft) length, or if in multiple pieces
connected together by the usual steel tie wires, exothermic
welding, welding, or other effective means to create a
6.0 m (20 ft) or greater length; or


It is the COMMON GROUNDING ELECTRODE for purposes of this discussion, as stated in the original post.